LED dies typically emit light over a very wide angle, typically up to 90 degrees off the center axis. It is common to redirect the light emitted by the LED using a lens or a reflective cup. Such simple optical techniques are adequate for devices used as indicator lights or where a precise emission pattern is not required.
When light from different color LEDs (e.g., RGB LEDs) needs to be mixed, such as for creating a white light, a typical technique is to mix the light in a diffusively reflective box having a light exit opening.
The above techniques have limited applications. An LED illumination system may consist of one or more LEDs (e.g., an array of LEDs) and both collecting and color combination optics. When the light output of an LED illumination system is narrowly specified for a system, innovative optical solutions must be used. The embodiments described herein are generally useful for étendue limited systems such as for projection displays (e.g., rear projection TV's or front projectors), automotive applications (e.g., headlights), fiber optics, accent lighting, color mixing in a compact space, and other applications.